State of the Art
Compound archery bows have been well known for many years. An early patent descriptive of such bows and their mode of operation is U.S. Pat. No. 3,486,495. Such bows are generally characterized by "let-off" leveraging devices carried at the distal ends of the limbs. These leveraging devices are usually referred to as wheels or pulleys, although they may take various forms, including some with other than circular cross-sections. They are commonly referred to as "eccentrics," because they characteristically are pivoted around an axle located off center with respect to their perimeters.
Archery bows of the type commonly known as "compound bows" are generally characterized by a pair of flexible limbs extending from opposite ends of a handle. The tips of the limbs are thus spaced apart in relationship to each other in a fashion similar to the limb tips of a traditional stick bow. The limbs are deflected by the operation of a bowstring in the same fashion as a traditional bow, but the bowstring is interconnected to the limbs through a rigging system including mechanical advantage-varying structures (including those commonly referred to as "eccentrics") and tension runs which transfer a multiple of the bowstring tension to the respective limbs. Tension runs are interchangeably and loosely referred to by those skilled in the art as "cables," "cable stretches," "bow string end stretches" and "end stretches." In any event, the rigging system may be regarded as a specialized block and tackle arrangement whereby pulling force applied to the bowstring is transferred to the limb tips to flex the limbs. The bowstring and tension runs may comprise a single continuous loop but, more typically, the bowstring is constructed of special bowstring material, while the tension runs are of more rugged construction, e.g. as from aircraft cable. The bowstring and tension runs together are referred to interchangeably as the "cable system," "cable loop" or "rigging loop."
The rigging of a compound bow functions as a block and tackle to provide a mechanical advantage between the force applied to the bowstring by an archer and the force applied to the bow limbs. In other words, in operation, the nocking point of the bowstring is moved a longer distance than the total distance that the two limb tips move from their braced position. Although other configurations are possible, an eccentric is usually pivotally mounted at each limb tip. If the eccentrics are mounted elsewhere, the rigging usually includes a concentric pulley at each limb tip.
Each eccentric has grooves or tracks analogous to the pulley grooves in a traditional block. A string track is arranged alternately to pay out or take up string as the limbs are alternately flexed to drawn or relaxed to braced condition. A cable track is arranged alternately to take up portions of the tension run as string is paid out while the eccentric pivots to drawn condition and to pay out portions of the tension run as string is wound onto the string track while the eccentric pivots to braced condition.
For purposes of this disclosure, it is recognized that in the operation of a compound bow, the portion of the rigging called the bowstring actually lengthens as the string is pulled back because as the eccentrics pivot from their braced condition, portions of the bowstring stored in the string tracks unwind and are paid out. Concurrently, portions of the tension run are wound onto the cable tracks of the eccentrics so that the tension runs decrease in length. The opposite phenomenon occurs as the string is released, permitting the eccentrics to pivot back to their braced condition. Assuming that the eccentrics are carried by the respective limb-tips, the portion of the rigging loop extending between points of tangency of the bowstring with the string track of the eccentrics will be referred to herein as the "central stretch" of the bowstring. The bowstring shall be considered to include, in addition to the central stretch, portions of the rigging loop stored at any time in association with the string tracks of the eccentrics. The portions of the rigging loop extending from the points of tangency of the tension stretches with the cable tracks of the eccentrics to remote points of attachment to the bow shall be called "end stretches." Each tension run is considered to include, in addition to an end stretch, the portion of the rigging loop extending from the end stretch and wrapped within or otherwise stored in association with the cable track of the associated eccentric.